This invention relates to ignition systems for small engine applications and, more particularly, to capacitor discharge ignition systems in which a microprocessor is provided to control the ignition timing of the system.
The ignition system of this invention is particularly adapted for small single cylinder internal combustion engines of the type commonly used for powering lawn mowers, chain saws, snow blowers, string trimmers and the like. It should, however, be understood that the invention is not necessarily limited to such application.
A capacitor discharge ignition or "CDI" system in the prior art of the type to which this invention would be applicable is disclosed in U.S. Pat. No. Re. 31,837 to Burson, assigned to the same assignee as this application.
U.S. Pat. No. 4,378,769 discloses the use of a microprocessor for digital control of an inductive type ignition system in which a transistor allows ignition current to flow through the primary winding of an ignition coil. When the current flow in the primary winding is interrupted, its collapse generates the ignition pulse in the secondary.
U.S. Pat. No. 4,515,118 also discloses a magneto ignition system of the inductive type.
The following U.S. patents disclose various magneto ignition systems controlled by microprocessors: U.S. Pat. Nos. 4,553,517; 4,570,595; 4,633,832; 4,653,189 and 4,656,985. These patents relate to inductive type ignition systems and employ reference pulses for the start and stop of the timer measuring function. In each of these patents, the reference pulses are generated in the ignition coil over successive complete revolutions of the rotatable permanent magnet poles of the magneto.
In the present invention, the ignition system is a capacitor discharge ignition system in which the start and stop, or reference, pulses for the time measuring function are both generated over only a portion of one revolution of the magneto.
It is the principal object of this invention to provide a capacitor discharge ignition system with a digital timing control in a system which is simple, economical and highly reliable.
It is another object of this invention to provide a CDI system of the above type wherein the pulses which charge the capacitor and which are used for the measurement of engine speed are all generated during a small part of one revolution of the engine and provide for timing advance at higher rpm.